### (12) 

# United States Patent Zecha et ai.

(54) SHEAR THINNING VINYLACETATE BASED POLYMER LATEX COMPOSITION, ESPECIALLY FORADHESIVES
(75) Inventors: Helmut Zecha, Burghausen (DE); RudolfWeissgerber, Burghausen (DE); Francis Petrocelli,Allentown, PA (US)
(73) Assignee: Air Products Polymers, L.P., Allentown, PA (US) 

### ( *) Notice: Subject to any disclaimer, the term ofthis patent is extended or adjusted under 35 U.S.c. 154(b) by 361 days.

(21) Appl. No.: 10/035,373 (22) (65)

(51)

(52)

(58)

(56)

DE 

### EP EP EP EP EP EP EP EP JP JP WO 

### Filed: Oct. 19, 2001
Prior Publication Data

US 2003/0109620 A1 

### Jun. 12, 2003


### Int. CI?

............ ... ............... C08F 2/38; C08J 3/00; C08K 5/05; C08K 3/20; C08L 11/02 U.S. CI.

......................... 526/85; 524/379; 524/387; 524/388; 524/457; 524/459; 524/503; 524/524; 524/556; 524/557; 524/563; 526/82 Field of Search

................................. 524/379, 387, 524/388, 457, 459, 503, 524, 556, 557, 563; 526/85, 82

References Cited
U.S. PATENT DOCUMENTS
4,128,518 A 5,391,608 A 5,434,216 A 5,439,960 A 

### * 12/1978 Oyamada et al.

........... 524/501 2/1995 Mudge et al.

.............. 524/459 7/1995 Mudge et al.

.............. 524/803 8/1995 Mudge et al.

..... ... ... ... 524/111


### FOREIGN PATENT DOCUMENTS

2620738 0322175 0433957 0501174 0561221 0623661 0686683 0812863 1170311 6322337 9302004 01/00695 12/1977 6/1989 6/1991 9/1992 9/1993 11/1994 12/1995 12/1997 1/2002 11/1994 11/1997 1/2001


### OlliER PUBLICATIONS
G. E. Ham, et aI., 

### VinylPolymerization, 1967, vol. I, Chap. 4, pp. 207-329. M. K. Lindemann, 

### The Mechanism ofVinylAcetate Polymerization. 

## 111111 1111111111111111111111111111111111111111111111111111111111111 US006794466B2

(10) 

## Patent No.: (45) 

## Date ofPatent: 

# US 6,794,466 B2 Sep.21,2004

H. Y. 

### Erbil, 

### Vinyl Acetate Emulsion Polymerization and Copolymerization withAcrylicMonomers, CRC Press 2000.

J. Brandrup, et aI., 

### Polymer Handbook, John Wiley Sons, Inc., 4th 

### Ed., 1999, P 11/97 ff.



### * cited by examiner



### Primary Examiner-Patrick D. Niland 

### (74) Attorney,Agent, or Firm-Mary E. Bongiorno
(57) ABSTRACT

Thepresentinvention elatesto avinyl acetate basedpolymer latex composition obtained by emulsion polymerization of:

(a) polyvinyl alcohol, (c) a monomer mixture comprising vinyl acetate, and (d)

optionally one or more additional co-monomer(s),

in presence of (c) 0.0001-0.05 wt. 

### % of a chain transfer agent, based on total monomer weight, said vinyl acetate based polymer latex composition having a weight average particle size**~400** 

### nm and a higher shear thinning factor than the vinyl acetate based polymer latex composition (a), (b) and (d) obtained in the absence of the chain transfer agent (c). According to one embodiment, emulsion polymerization is carried out in presence of0.001 to 0.05 wt. 

### % of a chain transfer agent selected from the group consisting ofaldehydes and chaintransfer agents having asimilarchain transfer constant with regard to vinyl acetate as the monomer. According to another embodiment, emulsion polymerization is carried out in presence of0.0001 to 0.01 wt. 

### % of

a chain transfer agent selected from the group consisting of thiols, mercapto acids, and chain transfer agents having a similarchaintransferconstantwithregardto vinyl acetate as the monomer. The invention also relates to an adhesive comprising said vinyl acetate based polymer latex composition. Such adhesive is preferably used in paper and packaging applications or as a wood working adhesive or wood glue.

The invention further relates to a process ofmanufacture of

a vinyl acetate based polymer latex composition having a weight average particle size >400 nm, including emulsion polymerization ofvinyl acetate in the presence ofpolyvinyl alcohol, optionally together with one or more additional co-monomer(s), wherein the emulsion polymerization is carried out in the presence of 0.0001 wt. 

### % to 0.05 wt. 

### % chain transfer agent, based on total monomer weight.

25 Claims, No Drawings

## US 6,794,466 B2 1
SHEAR THINNING VINYLACETATE BASED POLYMER LATEX COMPOSITION,

ESPECIALLY FORADHESIVES

BACKGROUND OF THE INVENTION 

## 2
adhesive obtained, especially its rheologicalproperties such

as viscosity and shear thinning, or the setting speed. Rheology mainly depends on the molecular weight distribution and degree ofhydrolysis ofthe polyvinyl alcohol used, but
5 can be changed by altering product recipe. For example, EP-A-0,686,683discloses altering the rheologicalproperties by altering the formulation with some thickening agent, thereby changing the continuous phase viscosity, at the Polymer emulsions or polymer latices prepared by conventional emulsion homo- or co-polymerization of vinyl acetate using polyvinyl alcohol as protective colloid are 10 widely used for adhesives. There are several application fields for such emulsions such as in wood glues, paper and packaging adhesives (e.g. case sealing, book binding, bag making, card board lamination), parquet adhesives and others. Most importantly these latices are used in paper and packaging or in woodworking adhesive formulations or wood glues. expense of an altered recipe. EP 00 114097.9, assigned to Air Products Polymers LP, discloses adjustment of rheological properties and expecially reduction of shear thinning of a latex emulsion by increasing particle size of the polymer without changing overall composition. More in detail, the document teaches
15 increasing particle size by carrying out emulsion polymerization ofvinyl acetate and optional co-monomers in presence ofa pre-crosslinking monomer selected from ethylenically unsaturated monomers such as triallyl cyanurate and allyl methacrylate. The document is silent on the possibility All these adhesives and especially woodworking adhesives are optimizedwithrespectto severalproperties such as waterresistance ofthe bond, heat resistance ofthe bond and creep of the bond. Further, before application several dispersionpropertiesmustbemet. These are compatibilitywith formulation aids such as film forming agents, fillers, metal salts; rheological properties; storage stability; the setting speed and so on. 20 of increasing shear thinning factor. With the term shear thinning the phenomenon of a viscosity drop with increased shear rate is addressed. Such decrease of viscosity is considered reversible if viscosity reaches the original value when the shear rate is decreased
25 to its original value. Vinyl acetate (VAc) based polymer latices for paper and packaging have to meet certain requirements regarding setting speed, penetration into the paper, open time, cohesionofthebond. Onthe otherhandtheyshouldpossessgood re-dispersability ofa film to provide good machine cleaning 30 properties. Shear thinning can be quantified by the so called "shear thinning factor" (SF) which is obtained as the ratio of viscosity measured by Brookfield viscosimeter at 1 rpm, Bf(l), and at 10 rpm, Bf(lO):

SF**~((Bfl/Bf1**0)-1). A shear thinning factor below zero (SF<O) indicates shear thickening, a shear thinning factor of zero (SF=O) indicates Newtonian behavior and a shear thinning factor above zero 35 (SF>O) stands for shear thinning behavior. Shear thinning factors;'O reflect properties of emulsions with high solids content as is typically the case for VAc based latices. Non-Newtonian behavior is in general no problem at lower VAc based polymer latices for woodworking adhesives having good water resistance typically use some functional post-crosslinking co-monomer in polymerization and the formulation with a catalyst afer polymerization. Amongst the post-crosslinkersN-alkylol derivativesofan amide ofan**a,~-ethylenically** unsaturated carboxylic acid, such as N-methylol acrylamide (NMA) which is preferred for latex wood glues are known. For example, U.S. Pat. No. 5,439, 960 and U.S. Pat. No. 5,391,608 describe the use of0.1 to 40 6% of NMA based on total monomer content Likewise European PatentApplication EP-A-0,561,221 describes the

use of 2 to 10% NMA. solids contents (e.g. below 40%). Itis an objectofthe presentinvention to find apossibility for independentcontrol ofthe shearthinning factor whichin turn allows to precisely and intentionally adapt the emulsion

or latex for certain applications thereby improving performance offor example a paper and packaging adhesive or of Asthe catalystfor formulation ofthe abovewoodworking adhesives having good water resistance water-soluble metal salts ofmonobasic acids such as aluminumm(III), chromium and/or zirconium(IV) salts, especially aluminum nitrate, chromium chloride or zirconium oxychloride are used (see for example DE-26,20,738, EP-A-0,433,957, EP-A-0,501, 174, EP-A-0,686,683 and U.S. Pat. No. 5,434,216).

Another approach to improve water resistance of wood glues is for example disclosed in EP-A-0,433,957, EP-A-O, 623,661 and lP-06,322,337 which documents relate to use of more hydrophobic co-monomers such as vinyl pivalate, diisopropyl maleate, diisopropyl fumarate, vinyl chloride or versatic acid vinyl esters for this purpose.

Adhesive performance of for example a wood glue is typically controlled bythe amount ofpolyvinyl alcohol, i.e. the ratio of polyvinyl alcohol to monomer, the polyvinyl alcohol molecular weight and its degree ofhydrolysis as for example disclosed in U.S. Pat. No. 5,434,216. In addition, functionalized polyvinyl alcohols, e.g. acetoacetylatedpolyvinyl alcohols or itaconic acid-modified polyvinyl alcohols,

or ethylene modified PVOH may be used.

The choice ofthe polyvinyl alcohol (PVOH) determines other properties of the vinyl acetate latex and thus the 45 a woodworking adhesive or wood glue. In several cases it would be especially useful and desirable to control shear thinning i.e. the shear thinning factor and to provide the desired extend ofit. More specifically, it would in the first place be desirable to avoid any shear
50 thickeningi.e. to be in the positionto shiftthe shearthinning factor from negative to positive values (SF>O). Performance requirements for a paper and packaging adhesive are, however, typically a SF within the range of**O.l<SF~l.5** dependent on the specific application, whereasperformance
55 requirements for awood glue are typically a SFin the range of**0.1<SF~0.6.** In any case shear thickening (SF<O) is preferably to be avoided.

Additionally, the requirementsfor setting speed and cohesion must be fulfilled: In the case of a paper and packaging
60 adhesive setting speed measured asAZG in seconds should be:<4 s, whereas cohesion measured at 70° C. should**be~4** N/mm2.

In the case of a woodworking adhesive (wood glue) the setting speed measured as bond strength after 2.5 minutes
65 gluing time should be>l.5 N/mm2. Cohesion of the wood bond measured as bond strength at 80° C. should be>6 N/mm2.

## US 6,794,466 B2 

## 3 4 together with one or more additional co-monomer(s), wherein the emulsion polymerization is carried out in the presence of0.0001 to 0.05 wt. % of a chain transfer agent, based on total monomer weight. Preferably the chain transOther useful adhesive performance parameters created e.g. bythe level ofco-monomer such as NMA, and/orbythe amount of PVOH and/or by its molecular weight and hydrolysis distribution, should remain more or less unchanged. 5 

### fer agents and the amounts used are as defined above.

It

### isthus anotherobjectofthe inventionto provide awood glue which meets the above requirements and has improved water resistance. Accordingto athird aspect thepresentinventionrelatesto
an adhesive, comprising the vinyl acetate based polymer latex composition as defined above.
BRIEF SUMMARY OF THE INVENTION The above objects are solved and the drawbacks of the prior art are overcome according to a first aspect of the invention by a vinyl acetate based polymer latex composition obtained by emulsion polymerization of: According to a preferred embodiment the adhesive is for
10 

### use as a fast setting adhesive for paper and packaging, said adhesive comprising a vinyl acetate homopolymer latex composition.

According to another preferred embodiment the adhesive is for use as awoodglue and comprises avinyl acetate based (a) polyvinyl alcohol, (b) a monomer mixture comprising vinyl acetate, and

optionally (d) one or more additional co-monomer(s), 15 

### polymer latex composition of a copolymer ofvinyl acetate/ N-methylol acrylamide, optionallyfurther includingversatic acid vinyl ester having 9 to 13 carbon atoms from the carbonic acid group. The chain transfer agent is preferably mercapto propionic acid. in presence of(c) 0.0001 to 0.05 wt. % (1 to 500 ppm) of a chain transfer agent (CTA), based on total monomerweight, saidvinyl acetate basedpolymerlatex composition having a 20 

### weight average particle**size~400** 

### nm and a higher shear thinning factor than the vinyl acetate based polymer latex composition obtained in the absence of the chain transfer agent.

According to a first embodiment the emulsion polymer- 25 

### ization is carried out in presence of0.001 to 0.05 wt. % of

a chain transfer agent selected from aldehydes, especially C2

_ 

### s-aldehydes and other CTAs having a similar chain transfer constant with regard to VAc as the monomer.

According to a second embodiment the emulsion poly- 30 

### merization is carriedoutinpresence of0.0001 to 0.01 wt. % DETAILED DESCRIPTION OF THE INVENTION The present invention is based on the surprising finding that the shear thinning factor of a vinyl acetate based polymer latex prepared by conventional emulsion polymerizationusing PVOH as aprotective colloid canbe increased without substantially changing the latex composition, especially without changing the type and/or amount of PVOH. This can be achieved by polymerizing the vinyl acetate in presence ofa small amount ofachain transfer agentwithout

a significant change ofthe average molecular weight, measured as the K-value. Thereby other important adhesive properties, such as cohesion,remainunchanged,whereasthe shear thinning may be adjusted as desired and/or a shear of a chain transfer agent selected from thiols, especially C2

_ 

### s-thiols, mercapto acids, especially C2

_ S

### -mercapto acids and otherCTAshaving a similarchaintransferconstantwith regard to VAc as the monomer. 35 

### thickening may be even reversed to shear thinning.

The latex ofthe inventionpreferably has a shear thinning factor of about 1,2 to 3,5 times the shear thinning factor of

alatex composition obtainedin absence ofthe chaintransfer agent or wherein the shear thinning factor is shifted from negative values to positive values as compared to the shear 40 

### thinning factor ofalatex compositionobtainedin absence of the chain transfer agent.

Preferably, the latex weight average particle size is about 60 to 95% the weight average particle size of a latex composition obtained in the absence of the chain transfer 45 

### agent.

Preferably, the chain transfer agent is selected from the group consisting of aldehydes, preferably C2

_ 

### s-aldehydes, thiols, preferably C2

_

### s-thiols, mercapto acids, preferably C2

_ 

### s-mercaptoacids, and mixtures thereof. More preferably 50 

### the chaintransfer agent is selectedfrom the group consisting of acetaldehyde, croton aldehyde, propionic aldehyde, 2-mercapto propionic acid, 3-mercapto propionic acid, and mixtures thereof.

The amount ofvinyl acetate is preferably in the range of 55 

### 100 wt. % to 60 wt. %, based on total monomer weight.

According to an especially preferred embodiment the vinyl acetate based polymer latex composition is a copolymer ofvinyl acetate/N-methylol acrylamide, optionally furtherincludingversatic acidvinylesterhaving 9to 13carbon 60 

### atomsfrom the carbonic acidgroup. The chaintransfer agent is then preferably a mercaptopropionic acid.

Accordingto a second aspectthepresentinventionrelates to aprocess ofmanufacture ofavinyl acetate basedpolymer latex composition having a weight average particle 65**size~400** 

### nm, including emulsion polymerization of vinyl acetate in the presence of polyvinyl alcohol, optionally More in detail, the invention to a first aspect thereofthus relates to a vinyl acetate based polymer latex composition obtained by emulsion polymerization of:

(a) polyvinyl alcohol, (b) a monomer mixture compnsmg vinyl acetate,

optionally (d) one or more co-monomer(s), and

in presence of(c) 0.0001 to 0.05 wt. % (1 to 500 ppm) ofa chain transfer agent, based on total monomer weight, said vinyl acetate based polymer latex composition having a weight average particle size**~400** 

### nm. The resulting VAc basedpolymerlatex compositionhas ahigher shearthinning factor than the VAc based polymer latex of the same composition (a), (b) and optionally (d) which is obtained in absence ofthe chaintransfer agent (c). Atthe same time, the K-value indicating molecular weight is surprisingly slightly increased or remains about comparable.

The use of a chain transfer agent (CTA) in emulsion polymerization ofVAc monomers is well known in the art and is described in textbooks, e.g. "Vinyl Polymerization", edited by George E. Ham, Marcel Dekker, 1967, Vol. I, 

### Chapter 4, pages 207-329: M. 

### K. Lindemann, "The Mechanism of Vinyl Acetate Polymerization" or "Vinyl Acetate Emulsion Polymerization and Copolymerization with Acrylic Momnomers" by H. Y. 

### Erbil, CRC Press 2000.

The latter textbook teaches that CTAs can be included in emulsion polymerization to terminate propagating polymer chains and to prevent polymer chains from growing too large, which may create problems in subsequent applications. Changingthe concentrationofsuchmodifiers or CTAs during emulsion polymerization leads to control of average

## US 6,794,466 B2 

## 5
molecular weight, molecular weightdistribution,branching, and crosslinkingofthepolymer.Theextendofchaintransfer

canbepredictedifthe chaintransferconstants C x areknown for a given monomer system. 

## 6 Astonishingly, these effects can be obtained for both VAC homopolymers and VAC copolymers comprising additional

co-monomers such as e.g. NMA, ethylene and/or versa tic acid esters. Chain transfer constants C x maybe obtained as explained 5 e.g. in the "Polymer Handbook", edited by J. Brandrup, E. The chain transfer agent for use in the invention may be selected from the group consisting of aldehydes, preferably C2-Cs-aldehydes, such as acetaldehyde, propionic aldehyde, butyraldehyde, croton aldehyde, and n-pentanal; thiols, preferably C2-Cs-thiols such as ethanthiol, H. Immergut, and E. A. Grulike, John Wiley Sons, Inc., 4. Edition, 1999, page 11/97 ff. Various transfer constants of vinyl acetate to different species are given there. Asknown radical transfer of a growing polymer chain may occur to any speciesinvolvedin the polymerization: monomer; polymer; protective colloid, such as PVOH; emulsifier, ifused; initiator; solvent, ifisused; or additives calledchaintransfer agents. Chain transfer constants of a certain species 

### (C x), may be different by several orders ofmagnitude in different

monomer systems.

ExamplesofCTAs used in VAc based latices include,but

are not limited to mercaptanes/thiols, aldehydes, chlorinated aliphatics and so on. The CTAs are usually characterizedby their chain transfer constant. To effect chain transfer CTAs

are typically used in appreciable amounts. For example EP 0,332,175 discloses the use of chain transfer agents in emulsionpolymerization ofVAc basedpolymerlatices. The specificchaintransfer agents described in saiddocument are usedin an amountof0.1 to 0.7wt. %. The resultingpolymer latices are disclosed to show an improved setting speed.

WO 01100 695 discloses a method for radically initiated, aqueous emulsionpolymerization for producing an aqueous polymer dispersion with polymer particles having a weight average particle**diameter~**300 nm. According to said method, atleast one monomerwith at least one ethylenically unsaturated group, preferably an acrylic monomer, is dispersedin an aqueousmedium andpolymerizedusing at least

one radical polymerization initiator in the presence of at least one radical chain transfer agent «5 wt. %) with a solubilitygreaterthan 1xlO-s molperkilogram water at 20° C. and at 1 bar (absolute). The resulting dispersions have a solids content of about 20-30 wt. %

When CTAs were used in emulsion polymerization, as given above (EP-A-0,322,175; JP-A-9,302,004; WO-A-Oll 00695; EP-A-0,812,863) it was accepted or it was even a goal (JP-A-9,302,004) that the molecular weight of the obtained polymer decreased. As is well known in the art, such drop ofmolecularweight has a negative impact on the cohesionofabondpreparedbysuchlowermolecularweight polymer. Only in few cases, e.g. for pressure sensitive adhesives, the lower molecular weight may influence tack and adhesion in the desired direction and the resulting loss of cohesion is acceptable.

It was surprising to find that, upon use of trace amounts 10 propanthiol, mercaptoethanol, 2- or 3-mercaptopropanol, lor 2-n-butane-thiol, and n-pentanethiol; and mercaptoacids, preferably C2

_ s-mercaptoacids, such as 2- or 3-mercapto propionic acid, and 2- or 3-mercapto butyric acid and mixtures thereof, mercapto acids being preferred. More
15 preferably the chain transfer agent used in the present invention is selected from the group consisting of acetaldehyde, propionic aldehyde, croton aldehyde, 2- and 3-mercaptopropionic acid, and mixturesthereof. Mostpreferably the chain transfer agent is a mercapto propionic acid
20 (MPA). Mixtures of CTAs may be used, provided the respective CTAs do not negatively interfere with each other.

The amount of CTAused according to the present invention is in general in the range of0.0001 to 0.05 wt % (1 to 500ppm),basedontotalmonomercontent,preferably0.001
25 to 0.05 wt. % (10 to 500 ppm). According to one embodiment the emulsion polymerization is carried out in presence of0.001 to 0.05 wt % (10 to 500ppm), preferably 0.001 to 0.02 wt. % and most preferably 0.001 to 0.01 wt. %, of a chain transfer agent selected from the group consisting of
30 aldehydes and CTAs having a similarchaintransferconstant with regard to VAc as the monomer. According to an alternate embodiment the emulsion polymerization is carried out in presence of0.0001 to 0.01 wt % (1 to 100ppm), preferably0.0001 to 0.005 wt. %, and mostpreferably0.001
35 to 0.0025 wt. %, of a chain transfer agent selected from the group consistingofthiols, mercapto acids, and CTAs having

a similar chain transfer constant with regard to VAc as the

monomer. All percentages are based on total monomer content. With the term "similar" as used above a chain
40 transfer constant is addressed which with regard to VAc under polymerization conditions is in the same order of magnitude and preferably only slightly differs from the one of an aldehyde, thiol and mercaptoacid, respectively.

The resulting polymer latex has a weight average particle
45 size**of~400** nm. Preferably suchparticle size isin the range of 500 to 1500 nm, more preferably 650 to 1500 nm, most preferably 700 to 1200 nm. Solids content of the emulsion is preferably equal to or above 40wt. %, more preferably in the range of45 to 70wt. %, most preferably in the range of
50 50 to 65 wt. %. At these high solids contents shear thinning

or thickening, which is of no concern for polymer latices containing less solids «40wt. %), needs to be paid careful attention. The shear thinning factor can be carefully and of a CTA, smaller final particle sizes are obtained which

causemore shearthinningorwhichmay even change ashear thickening behavior to a shear thinning one. At the same time, and even more surprisingly it was found, that latices polymerized in the presence oftraces of one or more CTAs 55 showed a clear tendency to faster setting speed. independently adjusted by the method of the invention. The CTA may be added to the initial reactor charge, before polymerization is started by adding the initiator, or may be fed to the reactor during the course ofthe polymerization. Conventional emulsionpolymerization maybe used

as e.g. described in EP 00 114097.9. For PVOH stabilized VAc based polymer latices, when used as adhesives, a too low molecular weight would decrease the cohesion of the bond. For these types of adhesives high cohesion is required, which should be also 60 sufficiently high enough at higher temperatures, named then

as heat resistance. CTAs are therefore generally considered disadvantageous in such compositions. The polymer latex of the invention comprises vinyl acetate as the base monomer. Vinyl acetate is used in an amount of 100to 60.0% byweight,basedon total monomer content. Preferably,the amountofvinyl acetateusedis inthe range of 100 to 80% by weight. According to one embodiIthas surprisingly and unexpectedlybeen discovered that the introduction oftrace amounts ofa CTAdid not decrease the molecularweight ofthe resulting polymer, characterized by the K-value, but that the opposite was observed. 65 mentthe VAc basedpolymerlatexmaybe a VAc homopolymer latex. These VAc homopolymer latices can advantageously be used for paper and packaging applications. The

## US 6,794,466 B2 7 

## 8
The aboveunsaturatedcarboxylic acid as the co-monomer is an ethylenically unsaturated acid and may be selected from the group consisting of acrylic acid, methacrylic acid, croton acid, itaconic acid, maleic acid, fulmaric acid, their VAc based latex compositlon may also be a co-polymer composition. In thiscase one ormore co-monomers selected from the following maybe copolymerizedwithVAc: one or
more post-crosslinking monomer(s), one or more vinyl ester(s), one or more ethylenically unsaturated acid(s) or anhydride(s) thereof, one or more acrylic acid(s), ethylene and mixtures of the foregoing. 5 

### anhydrides such as maleic acid anhydride, and mixtures thereof. If

### used, the amount ofthe ethylenically unsaturated carboxylic acid or their mixtures is 0.1 to 3.0% by weight, preferably 0.5 to 2.0% by weight, based on total monomer If e.g. designed for wood glues the vinyl acetate based polymer latex of the invention, preferably comprises a post-crosslinking monomer selected from the group consist- 10 

### ing of N-alkyol derivatives of an amide of an**a,~­** 

### ethylenically unsaturated carboxylic acid and mixtures thereof. Preferably the post-crosslinking monomer is selected from the group consisting ofN-Cl

_ 3

### -alkylol (meth) acrylamides, preferably N-methylol (meth)acrylamide, N-C l

_3 

### -alkylol melamides, preferably N-methylol melamide, N-Cl

_ 3

### -alkylol melamic acid and their esters, preferably N-methylol melamic acid, N-methylol melamic acid ester, N-C2

_ 

### s-acylol amides of vinylaromatic acids, N-Cl

_4

### -alkoxymethyl (meth)acrylamide, and mixtures thereof. More preferably, the post-crosslinking monomer is 20 

### N-methylol acrylamide (NMA).

With the term "(meth)acryl.

.." as used herein both the respective acrylic acid derivatives and the methacrylic acid derivatives are referred to. Thus, "N-methylol (meth) acrylamide" refers to both N-methylol acrylamide and N-methylol methacrylamide. The above Cl

_ 3 

### or Cl

_ 4 

### alkly residues include methyl, ethyl, n-propyl, i-propyl, n-, i-, and t-butyl residues and maybe chosenindependentlyfrom each other.

The post-crosslinking monomer is preferably comprised in the vinyl acetate based polymer latex composition ofthe invention in an amount of 0.1 to 5.0% by weight based on the total monomer content The post-crosslinking monomer
or mixtures of such monomers is known to be essential for sufficient water and heat resistance ofthe bond. Use ofsuch post-crosslinking monomer or monomer mixtures is therefore preferred. It 

### is, however, not necessary to achieve the effects of the invention. Therefore, although preferred, the post-crosslinking monomerisnot an essentialcomponentof the claimed latex composition.

The vinyl acetate basedpolymer latex composition ofthe invention may comprise the above one or more copolymerizable co-monomersinthe following amounts: up to 40%by weightvinylic ester, up to 15% byweight acrylic monomer, up to 3% by weight unsaturated carboxylic acid, and up to 30%byweightethylene, allpercentagesbeingbasedontotal

monomer content, or mixtures thereof, provided the total amount of copolymerizable co-monomers does not exceed 50% by weight. content. The vinyl acetate based polymer latex composition may further comprise up to 30% by weight ethylene, preferably 1 to 20% by weight ethylene based on total monomer contents. In apreferredembodiment, the vinyl acetate based polymer latex composition, which may optionally comprise
15 

### the above post-crosslinking monomer, comprises one or bothof 1to 20% byweightethylene and 1to 30%byweight vinyl ester as the copolymerizable co-monomers, provided the total amount of copolymerizable co-monomer does not exceed 1 to 40% by weight.

The colloidal stabilizer used in the vinyl acetate based polymer latex compositions of the invention is polyvinyl alcohol (PVOH). Various suitable polyvinyl alcohols are known to the skilled worker and are readily available. Especiallypreferred is apartially hydrolyzed PVOH having
25 

### adegree ofhydrolysis from 60 to 99 mol %, preferablyfrom 80to 97 mol %, mostpreferably 86 to 94 mol %. To achieve the desired viscosity level ofthe polymer latex and to allow for good adhesion performance of the bond, blends of different PVOH grades possessing different molecular
30 

### weights and hydrolysis distributions may be used. The colloidal stabilizer PVOH is typically used in an amount of 3 to 15% by weight, based on the total weight of the composition, more preferably 4 to 11% by weight.

As put forth above, the PVOH is typically chosen to 35 

### providedesiredperformance ofthe latex and/orthe adhesive comprisingthe same, respectively. Rheologicalproperties of the latex/adhesive likewise depend in part on the choice of the PVOH, but can be controlled independently by the use of CTAs according to the invention. This use of trace
40 

### amounts of CTAs according to the invention results in reduced shear thickening, in trans ferring a shear thickening into a shearthinning one, or in more shearthinning i.e. in an increased of the shear thinning factor SF. Such change of rheologicalpropertiesofvinyl acetatebasedpolymerlattices
45 

### using PVOH as the protective colloid, however, seemed to beimpossible withoutchangingthe amountorthe molecular properties ofthe PVOH The polymer latex particles may be co-stabilized by use of emulsifiers, if needed. These emulsifiers are known to the skilled worker and can be included Vinyl esters other than VAc which may be used in 50 

### combination with vinyl acetate are for example vinyl propionate, vinyl pivalate, vinyl laurate, vinyl 2-ethyl hexanoate, dibutyl maleate, dioctyl maleate, diisopropyl maleate, diisopropyl fumarate, versa tic acid vinyl esters having 9 to 13 carbon atoms from the carbonic acid group, 55 

### preferably 9 or 10 carbon atoms, or mieeuees thereof The amount ofothervinyl esters, ifused, is in the range ofup to 40.0% by weight, based on total monomer content, preferably 3 to 30% by weight. as usual. Preferably, non-ionic emulsifiers such as polyoxyethylene ethers or fatty alcohols may be used, preferably in

an amountof0.1 to 1.0%byweight,basedontotalmonomer content.

In a second aspect the present invention relates to a process of manufacture of a vinyl acetate based latex composition having a weight average particle**size~400** 

### nm, including emulsion polymerization of vinyl acetate in the presence ofpolyvinyl alcohol, optionally together with one
or more additional co-monomer(s), wherein the emulsion polymerization is carried out in the presence of0.0001 wt. % to 0.05 wt % of a chain transfer agent, based on total

monomer weight. The chain transfer agents(s) and the amounts used are as defined above. The acrylic monomer to be optionally comprised in the 60 

### vinyl acetate basedpolymer latex composition ofthe invention may for example be selected from the group consisting ofC1

_

### s-alkyl acrylates such as ethyl acrylate, butyl acrylate, 2-ethyl hexyl acrylate or mixtures thereof. The acrylic

monomer is preferably used in an amount ofless than 15% 65 

### byweightbased on total monomer content, more preferably in an amount of 1 to 10% by weight. The vinyl acetate basedpolymer latex composition ofthe invention may be obtained by conventional emulsion polymerization. Conventional batch or semi-batch emulsion polymerization procedures may be employed. Mainly for

## US 6,794,466 B2 

## 9 safety reasons and in view of the amount of heat to be dissipated, the semi-batch procedure is preferred. In case of

a semi-batch procedure a certain fraction of the reactants together with some water, if desired, and some of the polyvinyl alcohol solution as well as emulsifier solution, if 5 used, is initially charged to the reactor.

The reaction may be stated by feeding an aqueous solution of the initiator or initiator components. Preferred initiation of the emulsion polymerization of the invention is carried out by a redox reaction using a redox system of an 10 oxidant and a reductant in suitable amounts, the amount of initiator components to provide complete conversion depending on the selected initiator of the redox system. Typical oxidants are selected from the group of H2 

### 0 2, organic hydroperoxides such as t-butyl hydroperoxide (tBHP), inorganic persulfates such as sodium persulfate, 15 potassium persulfate and ammonium persulfate. Other organic peroxides may be used as well either alone or in combination therewith. Typical reductants are the sulfoxylates such as sodium formaldehyde sulfoxylate (SFS), sulfites such as sodium sulfite, sodium hydrogen sulfite, 20 dithionitessuch as sodiumdithionite, and organicreductants such as ascorbic acid and its derivatives. Preferred combinations are t-butyl hydroperoxide or hydrogenperoxide and sodium formaldehyde sulfoxylate (optionally in the presence oftraces offerro ammonium sulfate), t-BHP or H2 

### 0 2

- 25 and sodium sulfite, t-BHP or H2

### 0 2 and sodium hydrogen sulfite, t-BHP or H2

### 0 2 and sodium dithionite, t-BHP or H2

### 0 2and ascorbic acid, t-BHPorH2

### 0 2and erythorbic acid. Thermal initiation by H2

### 0 2 or other peroxides may also be applied. 30

Preferably, initiation of the emulsion polymerization is carried out by t-BHP or H2 

### 0 2 and SFS in the presence of traces of ferro ammonium sulfate. The initiator is used in suitable amounts to provide complete conversion of the

monomers. In case of the preferred initiation system typi

- 35 cally less than 0.015% by weight t-BHP, based on total

monomer content, for the course ofthe polymerization and less than 0.15% by weight t-BHP, based on total monomer content, for post-polymerization to reduce the residual

monomer content below 50 ppm, based on the emulsion, is 40 used. Molar ratios ofthe SFS are used during the course of the polymerization, typically, but are not desired. 

## 10
Final latex viscosity at 50% solids by weight will be between 1,000 and 40,000 mPas, mainly but not only depending on the type and amount of polyvinyl alcohol used. Viscosityismeasuredusing aBrookfieldviscometer at 20 rpm at 23° C.

The vinyl acetate basedpolymer latex composition ofthe invention thus obtained may be formulated into an adhesive by conventional means. In a third aspect the present invention thus relates to an adhesive comprising the above VAc based polymer latex composition. Optionally such adhesive may comprise suitable additives known to the skilled worker. Examples of such additives are plasticizers, antiblocking agents, film forming agents; water-soluble metal salts of monobasic acids such as aluminum, chromium and/or zirconium salts; free mineral acids such as hydrochloride acid, nitric acid, perchloric acid, phosphoric acid or mixtures thereofand antifoam agents (defoamers),biocides, and so on. For the use as a water resistant wood glue the formulation with metal salts, such as aluminum, chromium and/or zirconium salts; free mineral acids, such as hydrochloric acid, phosphoric acid or mixtures thereof is preferred.

The adhesives of the invention may be characterized as follows:
Paper and packaging adhesives:

A shear thinning factor SF in the range of**0.1<SF~1.5**

dependent on the desired application. A setting speed measured as AZG in seconds ofAZG<4

s. A cohesion measured at 70° C. of 24 N/mm2. Water resistant wood glues:

A shear thinning factor SF in the range of**0.1<SF~0.6.** A setting speed measured as bond strength after 2.5

minutes gluing time of>1.5 N/mm2. A cohesion measured at 80° C. of>6 N/mm2. Water resistance of a wood glue of performance group

D3: D3>2 N/mm2 and water resistance of a wood glue of performance group D4:**D3~4N/mm2** and**D4~4** N/mm2.
Properties oflatices were measured by the following test methods.

Test Methods

Latex Particle Size: Further on, the remaining fractions of the reactants, the PVOH solution as well as the emulsifier solution, if used, and extra water, if needed, are fed over a certain period of 45 time to the reaction vessel. Feeding rates will typically be kept constant over the feeding time, but may also vary, if desired. Typical reaction times depend on the reaction temperature and are typically within the range of2 hours to Final latexparticle size distributions were obtained either using the COULTER LS230, or using the COULTER N4,
50 both supplied by Coulter Cooperation, Miami, Florida 33196. Samplesofthe final latex were diluted to appropriate concentration using pure distilled water. 8 hours, preferably 4 hours to 6 hours.

The polymerizationreaction ofthe inventionispreferably performed at a temperature ranging from 50 to 90° 

### c., preferably between 60 and 80° 

### c., during most of the reaction time. Care has to be taken that an appropriate mixing of the components occurs in the reaction vessel. 55 Mixing is achieved by conventional means known to the skilled worker. Initial reactor charges and procedure can be chosen as needed.

The initiator components willbe fed to the reactor during all the reaction time, even after the feeding of reactants is 60 finished until nearly complete conversion is reached. The initiator feeding rate maybe keptconstant or mayvary over the time. For post-polymerization which is preferably carried outto reduce residual monomercontentbelow500ppm based on the latex, more concentrated solutions ofinitiator 65 components (preferably t- BHP/SFS) are fed to the latex. Finally the latex is cooled to ambient temperature. Coulter LS230 measurement is based on light diffraction combined with some static light scattering and provides a particle size distribution. As the larger particles are overestimated by this instrument, the median of the volume distribution function was chosen to characterize an average particle size.

Coulter N4 measurement is based on dynamic light scattering detected at 90 degrees scattering angle. The weight average was used to characterize particle size. Each value

was obtained as an average of 3 measurements.

Latex Viscosity and Shear Thinning: Latexviscosity was measuredusing Brookfieldviscosimeter. Viscosity data were taken for 1, 10 and 20 RPM. The latex viscosity is given for 20 RPM (Bf 20) in mPas. To

## US 6,794,466 B2 11
characterize the non-Newtonian behavior a shear thinning factor SF is calculated from the viscosity at 1 and 10 RPM: 

## 12

mm to 30mm i.e. 900 mm2

.The coatingweightofadhesive applied is 100 g each side. The specimens are put together and stored for 1 minute without pressure followed by a clamping pressure of 0.2 N/mm2 applied for a time of 30 SF=((Bfl/BflO)-l).A shear thinning factor SF>O indicates shearthinningwhereas SF<0 standsfor shearthickening.All measurements were carried out at 23° C.

Testing of K-value: A latex sample was one weighed to obtain 1 gram of polymer (notincludingthe PVOH). This sample wasdiluted with 5 ml ofpure water. 90 ml oftetra hydrofurane (THF)

were slowly added under stirring to give a clear polymer solution at room temperature. Additional pure water was then added to obtain a total amount of 100 ml solution. The viscosity ofthe homogeneous solution was estimated using 5 minutes. After a storage of 7 days at 23° C./50% reI. humidity, the test specimens were stored for 4 hours at a temperature of 70° C. in an oven preheated to 70° C. Directly following hot storage, the cohesion at 70° C. was determined in a tensile shear test, in which the bonded test
10 specimens were pulled apart using a tensile testing machine at apulling speedof50mm/min andwere stresseduntilthey broke. Onfracture, the maximum force F

### maxwhich occurred at that point was determined. The cohesion or thermal stability 1: is calculated from 1:=F

### maxlA, where A is the an Ubbelohde viscosimeter. Calculation of viscosity included the Hagenbach correction. The same was carried outfor asolutionrepresenting the solventincludingthe right amount of PVOH and 90 gram ofTHF. The "Eigenviscosity" k was then calculated based on the Fikentscher Equation. The K-value is then defined by K=103

### k. Itrepresents a simple viscosimetric average of the polymer molecular 20 weight. 15 bonded test area. Finalresults are meanvaluesfrom 6 single specimens and are given in N/mm2. Performance requirement is to achieve a bond**strengt~4** N/mm2.

Wood Working Adhesive Formulation: Baselatices,whichwerepolymerized asexplainedbelow,

were formulated to provide the wood working adhesive 25 formulation. Butyl carbitol acetate was used as a film forming agent (2,6 parts per 100 parts of latex). Alumium chloride hydrate was then added as a catalyst (3.5 parts of a 50% solution per 100 parts of emulsion for testing the D3-value, or 5 parts of a 50% solution for testing the 30 D4-values). The components were mixed at ambient temperature. The wood specimenswere gluedwithin 1to 5 days after preparation of the formulation.

Bond Strength in Accordance with DIN EN 204/205: Testing of Cohesion at 80° 

### c.: As test specimens,pairs ofbeechwoodpanelseach 5 mm thick, 125 mm wide and 325 mm long were bonded to one another using the respective adhesive dispersion, under a pressure distributeduniformly overthe bond area Following storage, the bonded panelswere divided into test specimens eachmeasuring 150mminlength and 20mminwidth.After the test specimens had been prepared they were stored at a temperature of 80° C. in an oven preheated to 80° C. Directly following hot storage, the thermal stability was determined in the tensile shear test on the lines ofDIN EN

Test specimens were produced in accordance with DIN EN 205. For this purpose pairs ofbeech wood panels, each 5 mm thick, 130 mm wide and 600 mm long, were bonded 205, in which the bonded test specimens were pulled apart using a tensile testing machine at a pulling speed of 50 mm/min and were stresseduntil theybroke. On fracture, the maximum force F

### max which occurred at that point was determined. The cohesion or thermal stability1: is calculated from 1:=F

### maxi A, whereA is the bonded test area Results are 35 given in N/mm2. Performance requirement is to achieve a bond**strength~6** N/mm2.

to one another with the adhesive formulation to be tested Testing the Setting Speed After 2.5 min Setting Time: In a manner similar to the procedure for testing the bond strength, pairs ofoakpanels each 5 mm thick, 20 mm wide and 150mmlongwerebondedusingthe respective adhesive dispersions, with a pressure distributed uniformly over the bond area. Thebond areawas20mm*20mm. Bond strength

was determined in the tensile shear test after 2.5 minutes, where after the bonded test specimens were pulled apart using a tensile testing machine at a pulling speed of 50 mm/min and were stresseduntil theybroke. On fracture, the maximum force F

### max which occurred at that point was determined, and was used in turn to determine the bond under a pressure distributed uniformly over the bond area and were stored in accordance with DINEN204. Following 40 storage, the bonded panelswere divided into test specimens each measuring 150mm in length, and these test specimens

wereused to determine the bond strengthinthe tensile shear test. In this test the bonded specimens were pulled apart using a tensile testing machine at a pulling rate of 50 45 mm/min and were stresseduntiltheybroke. On fracture, the maximum force F 

### max which occurred at that point was determined. Thebond strengthT iscalculated in accordance with DIN EN 205 from 

### T=FmaxlA, where A is the bonded test area Results are given in N/mm2. 50 strength at setting time t by 

### T,,=FmaxlA, where A is the bonded test area Results are given in N/mm2. Performance requirementisto achieve bondstrength>1.5N/mm2 after2.5 For testing of allocation to performance group D3, the specimens, after gluing, were storedunder standard climatic conditions (23° 

### c., 50% atmospheric humidity) for 7 days and then storedincoldwater at 20° C. for 4 days. Fortesting ofallocation to performance group D4, the specimens, after 55 gluing, were stored under standard climatic conditions (23° 

### c., 50% atmospheric humidity) for 7 days and then stored for 6 hours in boiling water, followed by 2 hours in cold water at 20° C. Allocationto performancegroup D3 requires to achieve a**D3-value~2** N/mm2.Allocationto performance 60 group D4 requires to achieve a**D4-value~4** N/mm2 and a**D3-value~4** N/mm2.

Testing of Cohesion at 70° C. mm. Testing the Setting SpeedAccording to theAZG-Method: During the setting of a dispersion based adhesive the strength ofthe bond increases. The setting can be described by measuring the change ofbond strength with time. In the AZG-Method the time is determined necessary that a bonding area of 1 cm2resists to a load of2 N applied vertical to the bond surface. For formation of the bond 50,u of the adhesive are applied to a standard cardboard and a 1 cm2 piece of cardboard is glued against the adhesive coating. After predetermined time the resistance ofthe bond against the load of2 N is testedAs result the bond resists or it fails. As test specimens, plywood panels (made from beech wood) each4 mmthick, 30mmwide and 135mmlongwere bondedto one anotherwith an overlapping length of30mm using the adhesive dispersion tested. The glued area is 30 65 The whole test is made in an automated device. The test procedure is repeated as often as necessary to find the shortest time needed to resist to the load of 2 N. This time

## US 6,794,466 B2 

## 13 14 Example 3 is called AZG value. Results are given in seconds. Perfor-

mance requirement is to achieve an AZG-value>4 s.

The following examples are given to further illustrate the present invention, but are not intended to limit the same.

EXAMPLES Same as example 1, but 25 PPM ofMPAbased on mass of VAC monomer was added to the initial reactor charge.
5 The final latex had a Brookfield viscosity of Bf20=6 500 mnPas. Setting speedwasimproved as indicatedbythe drop of the AZG-value compared to example 1. All examples given below were executed in a 3 I glass reactor, equipped with electronic temperature measurement and control, reflux condenser, and metering pumps for at 10 least four different feeds for parallel feeding. Mixing was achieved either by using an anchor-type stirrer at 150 rpm, constantly, or stirrer speedwas increased to 180rpm during the monomerfeed period. Fewexperimentswere carried out using a cross-beam type stirrer with inclined blades at 400 15 rpm.

The ingredients of the recipe were distributed among initialreactorcharge, feed 1,feed 2, feed 3,feed 4, andfeeds 5 and 6, if applied. The amount of the ingredients was chosen to give a final latex of 1800 to 2500 g. The initial 20 reactor charge was heated and feed 1 (and 2, if used) was (were) started at approximately 55° C. to initiate the reaction. Feeds 3 and 4 were started at 65° C. and were metered in during 50 to 180 minutes. Reaction temperature was maintained between 65 and 80° C. during the addition of 25 feeds 3 and 4. Itwasup to 80° C. to 90° C. for the last hour where the remaining feed 1 (and 2, if used) were added completely, after feeds 3 and 4 were finished

The free monomercontentbasedonlatex after the startof feeds 3 and 4 was controlled by appropriate addition rates 30 for feeds 1, 2, 3, and 4 to be between 2 to 15%. Feed 5 and 6, if applied, are added after feeds 1 and 2 have been completed. The product was cooled to ambient temperature under stirring at 100 rpm and application of a vacuum. If necessary, a small amount of defoamer was added. 35 Example 1 (Comparison A)
Initial reactor charge consisted of 29 parts of a 10% PVOH solution and 12.2 parts ofwater. PVOH used had a weight average of molecular mass distribution of Mw=103 40 000 g/Mol and a number average ofMn=50 400 g/Mol. The average degree of hydrolysis was 89%. pH value was adjusted to 5.8 by addition of0.02partsof 10% NaOH. 13.1 parts of a VAC monomer were added and finally 0.08 parts ofa 1 %Ferro ammon sulfate solutionwere addedjustbefore 45 the start of feed 1 and feed 2.

Feed 1consistedof2.7partsofa 0.3% hydrogenperoxide solution and feed 2 consisted of 2.7 parts of a 1.3% SFS solution. Feed3 consistedof40partsofVAC monomer. Post 50 polymerization was done by feeds 5 and 6 consisting of0.1 parts of a 10% tBHP and of 0.1 parts of a 10%0 SFS solution, respectively.

No other feeds were applied. The resulting latex (100 parts) provided a solid content of 56% for 100% monomer 55 conversion. Reaction was executed as given above. Final latex had a Brookfield viscosity ofBf20=2 600 mPas. Example 2 Example 4 (Comparison B)
Initial reactor charge consisted of 26 parts of a 10% PVOH solution and 16 parts ofVAC monomer. PVOHused had a weight average of molecular mass distribution of Mw=127 800 glMol and a number average of Mn=69 400 g/Mol. The average degree ofhydrolysiswas 87%. Reaction

wasstarted at 60° C. byadditionof0.08partsofa20% H2

### 0 2 solution.

Feed 1 consisted of2.2 parts of a 0.4% H2

### 0 2 solution. It

was started 5 min after the initial H2

### 0 2 addition together with feed 3. This feed 1was continuously charged for 480 min. Feed 3 consisted of46.3partsofVAC monomer. Itwas fed for 360 min. Feed 4 consisted of8.8 parts ofpure water whichwas started 60min after start offeed 3 andwhichwas metered in for 240 min.

Postpolymerizationwasdone by feeds 5 and 6 consisting of0.27parts ofa 10% tBHP and of0.27parts ofa 10% SFS solution, respectively. Both feeds were added after feeds 1 and 2 were completed and after a 1% ferro ammon sulfate (FAS) solution of 0.07 parts was added.

No other feeds were applied. The resulting latex (100 parts) provided a solid content of 65% for 100% monomer conversion. Reactionwasexecutedas given above. The final latex had a Brookfield viscosity of Bf20=33 500 mPas.
Example 5
Same as example 4, but 200 PPM ofcroton aldehyde was added to the initial reactor charge. The final latex had a Brookfield viscosity of 20 500 mPas.
Example 6
Same as example 4, but 400 PPM ofcroton aldehyde was added to the initial reactor charge. The final latex had a viscosity of Bf20=20 300 mPas.

Example 7 Same as example 4, but an effective amount of360 PPM of propionic aldehyde was added to the initial reactor charge. The final latex afterdilutionto 61.5% had aviscosity of 20 200 mPas. Example 8 (Comparison 

### C)
Initial reactor charge consisted of 37.9 parts of a 10% PVOH solution together with 6.7parts ofwater. The PVOH used had aweight average ofmolecularmassdistribution of Mw=149 200 glMol and a number average of Mn=94 600 g/Mol. The average degree ofhydrolysiswas91%. pHofthe aqueous solution was adjusted to 5.8 by addition of 0.05 parts ofa 10% NaOH solution InitialVAC monomer charge

was 12.3parts.Additionally0.05partsofa 1 % FAS solution Same as example 1, but 12.5 parts per million of 3-mercapto propionic acid (MPA) based on mass of VAC

monomer was added to the initial reactor charge. The final latex had a Brookfieldviscosity ofBf20=5 700 mPas. Shear thinning was improved, as indicated by the larger SF-value compared to example 1. Setting speed was improved as indicated by the drop of the AZG-value compared to example 1. 60 were added before starting the feeds 1 and 2. Feed 1 consisted of0.82parts ofa 0.25% TBHP solution, metered in for 200 min. Feed 2 consisted of 0.82 parts of a 0.38% SFS solution which was fed parallel to feed 1. Feed 3 consistedof36.6 partsofVAC monomerwhichwasfed in
65 for 160 min. Feed 4 consisted of 0.3 parts of N-methylol acryl amide together with 4.3 parts of water. This was fed parallel to feed 3.

## US 6,794,466 B2 15
Postpolymerizationwasdone byfeeds 5 and 6, consisting of0.1 parts of a 10% tBHP solution and 0.1 parts of a 10% SFS solution, respectively. The resulting latex (100 parts) provided a solid content of 53% for 100% monomer conversion Reaction was executed as given above. The final 5 

### latex, diluted to 50% solids, had a Brookfield viscosity of Bf20=5 920 mPas. Example 9

Same as example 8, but 25 PPM ofMPAwas fed within 10 

### feed 4 during the reaction. The final latex, diluted to 50%, had a Brookfield viscosity Bf20=5 730 mPas. Example 10
Same as example 8, but 45 PPM ofMPAwere fed within 15 

### feed 4 during the reaction. The final latex, diluted to 50%, had a Brookfield viscosity Bf20=6 090 mnPas. Example 11
Same as example 8, but 90 PPM ofMPAwere fed within 20 

### feed 4 during the reaction. The final latex, diluted to 50%, had a Brookfield viscosity Bf20=6 670 mnPas. Example 12 (Comparison D)
Same as example 8,but 180PPM ofMPAwere fed within 25 

### feed 4 during the reaction. The final latex, diluted to 50%, had a Brookfield viscosity Bf20=7 530 mPas. Example 13 (Comparison E) 30 

### Same as example 8,but360PPM ofMPAwere fed within feed 4 during the reaction. The final latex, diluted to 50%, had a Brookfield viscosity Bf20=6 870 mPas. 

## 16 PVOH was used as in example 16. pH of the aqueous solution was adjusted to 5.8 by addition of 0.01 parts of a 10% NaOH solution. Initial VAC monomer charge was 12 parts. Additionally 0.05 parts of a 1% FAS solution were addedjust before start of feeds 1 and 2.

Feed 1 consisted of 2 parts of a 0.25% tBHP solution, metered in for 200 min. Feed 2 consisted of 2 parts of a 0.38% SFS solution which was fed parallel to feed 1. Feed 3 consisted of 35.83 parts of VAC monomer and was metered in for 160 min. Feed 4 consisted of 0.9 parts of N-methylol acryl amide together with 3 parts ofwater. This

was fed parallel to feed 3.

Postpolymerizationwasdonebyfeeds 5 and 6, consisting of0.1 parts of a 10% tBHP solution and 0.1 parts of a 10% SFS solution, respectively. The resulting latex (100 parts) provided a solid content of 52.5% for 100% monomer conversion. Reactionwasexecuted as given above. The final latex, diluted to 50% solids, had a Brookfield viscosity of Bf20=16 730 mPas. Rheological behavior indicated strong shear thickening with a negative shear thinning factor SF.

Example 18

Same as example 17, but 25 PPM ofMPAwas fed within feed 4 during the reaction. Final latex, diluted to 50%, had

a Brookfield viscosity Bf20=10 060 mPas. The shear thickening behavior of example 17 was converted to shear thinning behavior.

Example 19

Example 14 (Comparison F)
Same as example 8,but720PPM ofMPAwere fed within feed 4 during the reaction. The final latex, diluted to 50%, had a Brookfield viscosity Bf20=5 400 mPas. Same as example 18, but monomer feed 3 comprised by
35 

### 95% ofVAC and 5% ofVeoVa9 monomer (ast supplied by Shell). The final latex, diluted to 50% solids, had a Brookfield viscosity of Bf20=9 050 mPas.

Example 15 (Comparison G) Example 20 (Comparison I)

40 

### Same as example 8, but instead of a anchor type stirrer a cross-beam type stirrerwith inclinedbladeswasused at 400 RPM. The final latex, diluted to 50% had a Brookfield viscosity Bf20=9 800 mPas. The rheological behavior clearly indicated shear thickening with a negative shear 45 

### thinning factor SF. Same as example 17, but monomer feed 3 comprised by 85% ofVAC and 15% ofYeoVa9 monomer. The final latex, diluted to 50% solids,had aBrookfieldviscosity ofBf20=10 800 mpas.
Example 21 Example 16
Same as example 15, but 25 PPM ofMPAwas fed within feed 4 during the reaction. The final latex, diluted to 50%, had a Brookfield viscosity Bf20=8 420 mPas. Shear thickening behavior of example 15 was converted to shear thinning behavior. Example 17 (Comparison H)
Initial reactor charge consisted of 37.1 parts of a 10% PVOH solution together with 6.9 parts ofwater. The same Same as example 20, but 25 PPM ofMPAwas fed within feed 4 during the reaction. The final latex, diluted to 50%
50 

### solids, had a Brookfield viscosity of Bf20=8 660 mpas.
Example 22

Same as example 21, but NMA content in feed 3 was 55 

### raised from 0.9 parts to 1.05 parts. The final latex, diluted to 50% solids, had a Brookfield viscosity of Bf20=8 000 mnPas.

## US 6,794,466 B2 17 18

TABLE 1

Latex and Adhesive Performance

final setting s12eed cohesion

particle paper wood wood wood erA size K s.c. Bf20 AZG 2.5 min 70° C. 80° C. Example PPM nm Value % mPas SF N/mm2 N/mm2 N/mm2

lA 0 1187 ') 115 56 2600 0.65 2 12.5 A) 932') 134 56 5700 1.13 3 25.0 A) 907 ') 132 56 6500 1.19 4B 0 1551 2) 112 65 33500 0.80 5 200 B) 1357 2 ) 113 65 20500 0.92 400 B) 11122) 107 65 20300 1.02 7 360 C) 1283 2) 96 61.5 20200 lAS 8C 0 935 ') 136 50 5920 0.25 9 25 A) 822') 142 50 5730 0.30 10 45 A) 777 ') 135 50 6090 0045 11 90 A) 760 ') 117 50 6670 0.54 120 180 A) 743 ') 102 50 7530 0.64 BE 360 A) 1050 ') 91 50 6870 0.39 14 F 720 A) 1045 ') 76 50 5400 0040 15 G 0 1440 ') 134 50 9800 -0.16 16 25 D) 1020 ') 145 50 8420 0.15 17H 0 1950 2) 136 50 16730 -0.24 18 25 A 1050 2) 131 50 10060 0.21 19 25 A) 1236 2) 123 50 9050 0.15 20 I 0 1176 2) 119 50 10800 0.08 21 25 A) 1226 2) 124 50 8660 0.21 22 25 A) 1170 2) 126 50 8000 0.31

A)CTA 3-mercato propionic acid B)erA croton aldehyde C)erApropion aldehyde D)CTA 2-mercapto propionic acid '>particle size median X 3•50 from COULTER LS 230 analysis 2>particle size weight average from COULTER N4 analysis

Example

9 10 11 16 18 19 21 22 

### TABLE 2

Wood Glue Performance

03-value N/mm2

2.8 3.0 2.9 2.3 304 3.9 5.3 5.5 04-value N/mm2

1.8 3.1 3.0 4.1 4.0 6.0 3.8 3.0 5.7 2.7 3.7 3.5 1.5 1.9 2.0 2.0 2.1 2.3 2.0 1.5 1.8 1.1 2.0 204 1.7 2.8 2.2 4.6 404 4.3 4.5 4.5 4.2 4.0 7.2 7.0 7.2 6.5 5.5 5.1 5.2 7.2 7.3 704 7.5 7.2 6.8 7.1 7.1

35 

### (SF<O) to a shear thinning one (SF>O) within the desired range ofSF. At the same time the setting speed is improved without impairing cohesion.

Additionally, the results of the comparative Examples 12D, 13E, 14F demonstrate, that use of a CTA above the
40 

### limits ofthis invention in accordance with the prior art will result in a much higher decrease of the average molecular weight, expressed as the K-value, and will thereby contribute to an unacceptable loss or reduction of cohesion.

Examples 21 and 22 represent VAC co-polymers suitable
45 

### as a base of high performance boiling water resistant D4 wood glues. Comparing Examples 21 and 22 with 20Lboth the setting speed and the shearthinning are improvedbyuse trace amounts of aCTA.

We claim: In Table 1 the results ofthe 13 examples, and 9 compara- 50 

### tive examples are summarized. Table 2 summarizes results obtained for the water resistance of the bond when base emulsions obtained in the framework ofthis invention were formulated as wood glues. 1. 

### Vinyl acetate based polymer latex composition obtained by emulsion polymerization of:

(a) polyvinyl alcohol, (c) a monomer mixture comprising vinyl acetate, and (d)

optionally one or more additional co-monomer(s), Examples 2, 3, 5, 6, and 7 represent VAC homopolymer latices ofthis invention prepared in the presence ofPVOH. The comparisonwithExample 1reveals that the use oftrace amounts of CTA results in the following: the setting speed measured as AZG is considerably increased, the shear thinning may be adjusted within the required range, cohesion stays within its desired range and K-value is slightly increased or remains about unchanged.

Examples 9, 10, 11, 16, 18, 19, 21, and 22 represent VAC co-polymers suitable as base of high performance water resistant D3 wood glues. Comparing Example 16 with 15G, and 18 with 17H it is obvious that the use oftrace amounts of a CTA may even convert a shear thickening behavior 55 

### in presence of (c) 0.0001-0.05 wt. 

### % of a chain transfer agent, based on total monomer weight, said vinyl acetate based polymer latex composition having a weight average particle size**~400** 

### nm and a higher shear thinning factor than the vinyl acetate based polymer latex composition (a),
60 

### (b) and (d) obtained in the absence of the chain transfer agent (c).

2. Composition according to claim 1, wherein emulsion polymerizationiscarried outinpresence of0.001 to 0.05wt. 

### % ofa chain transfer agent selected from the group consist65 

### ing of aldehydes and chain transfer agents having a similar chain transfer constant with regard to vinyl acetate as the

monomer.

## US 6,794,466 B2 

## 19
3. Composition according to claim 1, 

### wherein emulsion polymerization is carried out in presence of0.0001 to 0.01 wt. % of a chain transfer agent selected from the group consisting of thiols, mercapto acids, and chain transfer agents having a similar chain transfer constant with regard to vinyl acetate as the monomer.

4. Composition according to claim 1, 

### having a shear thinning factor of about 1,2 to 3,5 times the shear thinning factor of a latex composition obtained in absence of the chain transfer agent or wherein the shear thinning factor is shifted from negative values to positive values.

5. Composition according to claim 1, 

### wherein the latex weight average particle size is about 60 to 95% the weight average particle size of a latex composition obtained in the absence of the chain transfer agent.

6. Composition according to claim 1, 

### wherein the chain transfer agent is selected from the group consisting of C2

_ 

### s-aldehydes, C2

_ 

### s-thiols, C2

_

### s-mercaptoacids, and mixtures thereof.

7. Composition according to claim 2, wherein the chain transfer agent is selectedfrom the group consistingofcroton aldehyde, propionic aldehyde, and mixtures thereof. 

## 20
14. Composition according to claim 13, wherein the post-crosslinking monomer is N-methylol acrylamide.

15. Composition according to claim 8, wherein the vinyl acetate based polymer latex composition is a copolymer of
5 

### vinyl acetate/N-methylol acrylamide, optionally further including versa tic acid vinyl ester having 9 to 10 carbon atoms from the carbonic acid group.

16. Process of manufacture of a vinyl acetate based polymer latex composition having a weight average particle
10 

### size**~400** 

### nm, including emulsion polymerization ofvinyl acetate in the presence of polyvinyl alcohol, optionally together with one or more additional co-monomer(s), wherein the emulsion polymerization is carried out in the presence of0.0001 wt. % to 0.05 wt. % chain transfer agent, 15 

### based on total monomer weight. 17. Process according to claim 16, wherein emulsion polymerizationiscarried outinpresenceof0.001 to 0.05wt. % ofa chain transfer agent selected from the group consisting of aldehydes and chain transfer agents having a similar
20 

### chain transfer constant with regard to vinyl acetate as the

monomer.

8. Composition according to claim 3, wherein the chain transfer agent is selected from the group consisting of 2-mercapto propionic acid, 3-mercapto propionic acid, and 25 

### mixtures thereof. 18. Process according to claim 16, wherein emulsion polymerization is carried out in presence of0.0001 to 0.01 wt. % of a chain transfer agent selected from the group consisting of thiols, mercapto acids, and chain transfer agents having a similarchain tansfer constant withregard to vinyl acetate as the monomer. 9. Composition according to claim 1, 

### wherein the amount ofvinyl acetate is in the range of 100 wt. % to 60.00 wt. %, based on total monomer weight. 10. Composition according to claim 1, 

### wherein the polyvinyl alcohol has a degree of hydrolysis from 60 to 99 mole-% and is present in an amount of3 wt. % to 12wt. %, based on total monomer weight. 19. Process according to claim 17, wherein the chain transfer agent is selectedfrom the group consistingofcroton
30 

### aldehyde, propionic aldehyde or mixtures thereof.

11. Composition according to claim 1, 

### wherein the vinyl acetate based polymer latex composition further comprises 35


### one or more co-monomers selected from the group consisting of one or more vinyl ester(s), other than vinyl acetate,
one or more post-crosslinking monomer(s), one or more ethylenically unsaturated acid(s) or anhydride(s) thereof,

one or more acrylic monomer(s), and mixtures thereof. 40



### 12. Composition according to claim 11, 

### wherein the one
ormore vinyl ester(s) are selectedfrom the group consisting 20. Process according to claim 18, wherein the chain transfer agent is selected from the group consisting of 2-mercapto propionic acid, 3-mercapto propionic acid or mixtures thereof.

21. Process according to claim 16, wherein the vinyl acetate based polymer is a co-polymer of vinyl acetate/Nmethylol acrylamide, optionally fierier including versatic acid vinyl ester having 9 or 10 carbon atoms from the carbonic acid group, and the chaintransfer agentismercapto propionic acid.

22.Adhesive, comprisingthe vinyl acetate basedpolymer latex composition according to claim 1. ofvinyl propionate, vinyl pivalate, vinyl 2-ethyl hexanoate, diisopropyl maleate, diisopropyl fumarate, versa tic acid vinyl esters having 9 to 10 carbon atoms from the carbonic acid group, and mixturesthereof, the one or more additional vinyl ester(s) being present in an amount ofup to 40 wt %, based on total monomer weight. 23.Adhesive, comprisingthe vinyl acetate basedpolymer
45 

### latex composition according to claim 15.

13. Composition according to claim 11, 

### wherein the one
or more post-crosslinking monomer(s) are selected from N-alkoyl derivatives of an amide of a**a,~-ethylenically** 

### unsaturated carboxylic acid. 24. Adhesive according to claim 22, for use in paper and packaging, comprising a vinyl acetate homopolymer latex composition.

25. Adhesive according to claim 23 for use as a wood
50 

### glue.


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